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61'StreetRat
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Joined: December 14, 2011
Posts: 45
Location: Reno
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 Posted: Sun Mar 17, 2013 10:07 pm Post subject: Crank Case Ventelation/Oil Breather |
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So it's spring! I'm doing my routine maintaine on my engine. It is a 1915cc. Dual 40 Kad's with an Engle 110. Heads are ported, mild.
I have a bugpack oil breather I found in the garage, and don't think it is necessary to have on my engine. I was running a hose from the oil filler neck straight towards the ground. Now I'm thinking of running a hose from the oil filler neck to the carb on the right. What's everyone's opinion? Should I use that bugpack oil breather? Or go with the stock design of running it straight to the carb?
P.S. I've looked through the other post & google. Still cannot come to a conclusion on how useful that breather is. It seems to me that the engine vents fine at the oil filler neck. |
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spyvsspy
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Joined: August 22, 2006
Posts: 1022
Location: inside the barrel...
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| Posted: Sun Mar 17, 2013 10:48 pm Post subject: |
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Is the block leaking oil? It never hurts to vent the valve covers...
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61'StreetRat
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Joined: December 14, 2011
Posts: 45
Location: Reno
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| Posted: Sun Mar 17, 2013 11:21 pm Post subject: |
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| No leaks what so ever. What benefit is there to vent the valve covers? |
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spyvsspy
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Joined: August 22, 2006
Posts: 1022
Location: inside the barrel...
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| Posted: Sun Mar 17, 2013 11:36 pm Post subject: |
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Venting the case relieves the internal pressure which causes the oil to blow by seals, etc. Venting to the carbs also burns gasses from the oil...
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Eaallred
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Joined: May 18, 2003
Posts: 5756
Location: West Valley City, Utah
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| Posted: Mon Mar 18, 2013 7:14 am Post subject: |
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I don't vent valve covers anymore. I've found a bigger/better breather off the case (alt/gen stand) relieves as much pressure as you could need.
Pressure isn't forming out at the heads under the valve covers, it's building in the case. Vent the case. Venting valve covers means you are forcing the air from the case, up the pushrod tubes, then out the valve cover. Why make it travel so far? Venting at the source is more effective.
V8's vent valve covers because that's the highest point of the engine, and frankly, the only place at the top of the engine to really put a vent. VW guys (myself included) are/were venting valve covers in a monkey-see monkey-do fashion. I've learned the valve cover venting is pointless if you have an adequate vent on the case. If it works for my race motor, it will work for your street motor.
But some will argue. This is just what I've found works.
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Eric Allred
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VIN
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Location: phoenix
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andk5591
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Joined: August 29, 2005
Posts: 16800
Location: State College, PA
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| Posted: Mon Mar 18, 2013 7:50 am Post subject: |
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Having some sort of filter element at the end of the vent hose is a good idea. I attached a PCV elbow fitting to the right air cleaner on a couple of my cars.
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There's more, but not keeping them... |
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hill
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Joined: September 24, 2011
Posts: 442
Location: PNW
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| Posted: Mon Mar 18, 2013 8:00 am Post subject: |
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| Eaallred wrote: |
I don't vent valve covers anymore. I've found a bigger/better breather off the case (alt/gen stand) relieves as much pressure as you could need.
Pressure isn't forming out at the heads under the valve covers, it's building in the case. Vent the case. Venting valve covers means you are forcing the air from the case, up the pushrod tubes, then out the valve cover. Why make it travel so far? Venting at the source is more effective.
V8's vent valve covers because that's the highest point of the engine, and frankly, the only place at the top of the engine to really put a vent. VW guys (myself included) are/were venting valve covers in a monkey-see monkey-do fashion. I've learned the valve cover venting is pointless if you have an adequate vent on the case. If it works for my race motor, it will work for your street motor.
But some will argue. This is just what I've found works. |
Good info - thanks for putting it out here Erik even though it's like you might have kicked a hornet's nest.
Do you rely on intake 'suction' to positively vent your case(s) or just count on an opening to make an escape for the building pressure? Do you think it'd be enough relief for an engine that would run longer than it takes to stage and make a run - an engine putting around in traffic on it's way to a long freeway jaunt?
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Eaallred
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Joined: May 18, 2003
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Location: West Valley City, Utah
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| Posted: Mon Mar 18, 2013 8:07 am Post subject: |
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| VIN wrote: |
| Eric, what breather are you using? |
I've moved up to a vacuum pump system now, but I've used a big breather box made of ABS plumbing from the hardware store, I built a large box that was baffled out of metal, I've done 1/2" and 3/4" breather lines off the case and valve covers. I've tried everything I could think of on my race motor to control case pressure the most efficient way. What it all came down to, was venting valve covers was a waste of time.
Venting the 3/4 valve cover always ended up being nothing but trouble for me. Pushing oil out of the vent. I added two 3/4" drain lines from the valve cover down to the sump to alleviate the issue, but only helped so much. Eliminating the vent on 3/4 side ended up working the best. I had a 3/4" breather from the alt stand to the box, and what was basically a drain line from the box down to the 1/2 valve cover (probably not needed). Bigger vent on case, and eliminating vent on 3/4 valve cover allowed me to get rid of my two 3/4" drain lines from the 3/4 valve cover too. At that point, I was able to control the oil issues at high rpms at the track. But then a vacuum pump system came up for sale for a great price, so I jumped on it.
Granted, it's a race car, but spinning big rpms (9,000) and finding what works in the extremes will certainly show you what will work for street applications.
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Eric Allred
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laker
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Joined: July 31, 2012
Posts: 196
Location: So. Cal
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| Posted: Mon Mar 18, 2013 8:23 am Post subject: |
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| Eaallred wrote: |
| VIN wrote: |
| Eric, what breather are you using? |
I've moved up to a vacuum pump system now, but I've used a big breather box made of ABS plumbing from the hardware store, I built a large box that was baffled out of metal, I've done 1/2" and 3/4" breather lines off the case and valve covers. I've tried everything I could think of on my race motor to control case pressure the most efficient way. What it all came down to, was venting valve covers was a waste of time.
Venting the 3/4 valve cover always ended up being nothing but trouble for me. Pushing oil out of the vent. I added two 3/4" drain lines from the valve cover down to the sump to alleviate the issue, but only helped so much. Eliminating the vent on 3/4 side ended up working the best. I had a 3/4" breather from the alt stand to the box, and what was basically a drain line from the box down to the 1/2 valve cover (probably not needed). Bigger vent on case, and eliminating vent on 3/4 valve cover allowed me to get rid of my two 3/4" drain lines from the 3/4 valve cover too. At that point, I was able to control the oil issues at high rpms at the track. But then a vacuum pump system came up for sale for a great price, so I jumped on it.
Granted, it's a race car, but spinning big rpms (9,000) and finding what works in the extremes will certainly show you what will work for street applications. |
Erick can you post a picture of how you tapped your Alternator Stand for reference? |
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MotoGreg
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Joined: January 10, 2012
Posts: 148
Location: Ladera Ranch, CA
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| Posted: Mon Mar 18, 2013 8:30 am Post subject: |
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Eric, I agree. From what I've always known, when the pistons come down on the power stroke it pressurizes the crankcase under the piston. In theory (well, in my mind at least) it seems like there is always a piston rising, while another is coming down... so the air volume inside the block should just be shifted around, back and forth from the hi-pressure area (under the downward piston) to the low pressure area (under the rising piston) and maintain an equal pressure within the case/block. However, as we know, it doesn't work that way and pressure does indeed build up in the block.
I can't see any reason why pressure would build up in the valvecover area. There is nothing there to cause a pumping action. Granted if your block isn't adequately vented then the pressure has to go somewhere, and it will find its way past the lifters and down the tubes into the valvecovers... but no pressure was produced there.
One question: Do you modify that vented metal shim that sits between the alt. stand and the case? Or do you leave it intact as is? |
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Eaallred
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Joined: May 18, 2003
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Location: West Valley City, Utah
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| Posted: Mon Mar 18, 2013 8:36 am Post subject: |
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I've left the stock baffle under the alt stand intact.
For the alternator stand, I took a new oil filler nut, and welded on either a -12 AN male bung, or a short piece of 3/4" pipe to attach a hose to.
It makes filling oil a bit more work, but I don't have to top off oil like I used to either.
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Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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hill
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Joined: September 24, 2011
Posts: 442
Location: PNW
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| Posted: Mon Mar 18, 2013 9:54 am Post subject: |
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I wonder if it would be informative to install a pressure gauge on an engine case.
MotoGreg - I've thought it's different than your model. Instead of the upward piston equalizing pressures created by the opposing downward piston I think the upward piston acts like a suction pump drawing in more air to be pumped up, maybe through the rear crank slinger.
With more air the pressure keeps rising relieved by exceeding the suction of rising pistons and pushing back out through the open rear slinger. When it gets higher than can be relieved that way it starts pushing through anyplace it can and then starts making a mess by pushing through seals and anywhere else it can escape.
The crankcase and valve covers, pushrod tubes, etc. are one enclosed volume of air pressurized by the pumping action of pistons. When the volume is pumped up anywhere it can be relieved will help, including the valve cover vents. Without some auxiliary method to take off pressure, like Erik's vacuum pump, anywhere a relief vent can be established will help.
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jd-drafter
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Joined: June 10, 2006
Posts: 197
Location: northern az
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| Posted: Mon Mar 18, 2013 2:51 pm Post subject: |
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recent experience...
my beater bug... 68' with stock "h" case singleport- and stock oil bath air cleaner-
a buddy of mine (vw guy) borrowed the car for a while and replaced the stock oil bath ac with an aftermarket paper/gauze cone type filter (plugged the stock vent on top of the filler). when i went to get it back i noticed some oil under it..and a little under the decklid.
upon driving home my wife followed and said it was smoking when i got on it in 3rd and 4th gear. did not see anything at that point... let the son in law drive it and it came back a mess-
looked like it was spewing oil from the crank pulley? my buddy was convinced that it must be a leak... i was convinced it was from crank case pressure... he maintained that the drain tube from the filler nack was plenty of venting.
so he kept it another week- pulled the engine- stripped the engine down thinking it might have been the oil cooler- dry as a bone. reinstalled engine... i was there and replaced aircleaner with stock and hooked the vent tube up again... while firing it up o placed a finger near the vent tube... and there is a good amount of air leaving that case!
since installing the stock AC and venting... not a single leak... |
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Eaallred
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Joined: May 18, 2003
Posts: 5756
Location: West Valley City, Utah
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| Posted: Mon Mar 18, 2013 5:41 pm Post subject: |
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Did the tube going down have the draft tube rubber end on it? That would cause what you described.
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Eric Allred
You have to remember something: Everybody pities the weak; Jealousy you have to earn. |
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longboard511
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Joined: August 21, 2012
Posts: 133
Location: england
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| Posted: Tue Mar 19, 2013 6:28 am Post subject: |
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running -10 breather off the fuel pump blank to a pot under the wing and no issues here
blocked the valve covers off that the po vented
there is no point the pressure is in the crankcase not the heads |
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shokwave2
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Joined: February 02, 2010
Posts: 264
Location: Wollongong, Australia
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| Posted: Tue Mar 19, 2013 4:43 pm Post subject: Re: Crank Case Ventelation/Oil Breather |
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| 61'StreetRat wrote: |
So it's spring! I'm doing my routine maintaine on my engine. It is a 1915cc. Dual 40 Kad's with an Engle 110. Heads are ported, mild.
I have a bugpack oil breather I found in the garage, and don't think it is necessary to have on my engine. I was running a hose from the oil filler neck straight towards the ground. Now I'm thinking of running a hose from the oil filler neck to the carb on the right. What's everyone's opinion? Should I use that bugpack oil breather? Or go with the stock design of running it straight to the carb?
P.S. I've looked through the other post & google. Still cannot come to a conclusion on how useful that breather is. It seems to me that the engine vents fine at the oil filler neck. |
I'm running a 2054cc, also with Dual 40 Kad's and Engle 110. I was running my breather hose down through the tinware towards the ground, then eventually ran it to the right carb using a elbow joint as mentioned.
I've had no overheating or pressure problems since building the motor over 6 months ago. Just make sure not to overfill with oil as this excess oil can be blown up to your carb and foul your plugs.
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vwracerdave
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| Posted: Tue Mar 19, 2013 5:27 pm Post subject: |
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On a high RPM race engine you need to vent the valve covers so air can enter and the oil can return faster to the case through the push rod tube without burping and gurgling air. Turn a bottle of soda upside down and watch how it burps air to flow out the bottom. Now punch a small hole on the top of the bottle and the soda will flow right out quickly.
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builtbychevy
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Eaallred
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Joined: May 18, 2003
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Location: West Valley City, Utah
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| Posted: Thu Mar 21, 2013 9:17 pm Post subject: |
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| vwracerdave wrote: |
| On a high RPM race engine you need to vent the valve covers so air can enter and the oil can return faster to the case through the push rod tube without burping and gurgling air. Turn a bottle of soda upside down and watch how it burps air to flow out the bottom. Now punch a small hole on the top of the bottle and the soda will flow right out quickly. |
Sorry Dave, but I couldn't disagree more. My findings were with my high rpm race motor (rev limiter set at 9300rpm).
The higher the rpm, the more issue I had with valve cover vents.
Eliminated the vents at the valve covers, increased the vent at the case, and zero issues after that.
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Eric Allred
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